The U.S. Supreme Court agreed Friday to hear a trucking industry challenge to an ambitious environmental regulation program at the Port of Los Angeles, a move that could signal the court's intention to throw out key facets of the port's policies.

The high court will hear a case brought by the American Trucking Associations involving several facets of the port's Clean Trucks Program, which began in 2008 and restricts many older, less environmentally friendly trucks from hauling goods to and from the port. Lawyers for the trucking industry have argued the port and city of Los Angeles do not have broad authority to regulate trucking companies. They say that power rests almost entirely with the federal government.

In 2011, the U.S. 9th Circuit Court of Appeals sided with the port on most of key issues, ruling it could institute a policy - called a concession program - under which trucking companies would be held liable for certain truck maintenance, insurance, security and safety measures.

Under the concession program, truck companies must register to operate at the port, and, in rare cases, they can have their licenses revoked. As a matter of law, the appeals court found the port has a right - one not superseded by federal statute - to act as any privately owned port firm would and impose conditions regarding which truck companies can access its facility.

The appeals court struck down a requirement that would have forced trucking companies operating at the port to employ drivers. That part of the opinion allowed many trucking companies to continue using independent contractors as drivers. (Afterward, the port dropped the employer requirement, and it is no longer part of the litigation.)

Had the U.S. Supreme Court not agreed Friday to take the case, the 9th Circuit's decision allowing the concession program would have stood, and this legal challenge would have ended.

While the Supreme Court could ultimately hear the case and agree with the appeals court, the fact that the justices decided to get involved could signal they plan to overturn part or all of the lower court's decision, said Scott Cummings, a professor at UCLA School of Law.

"What the court will ultimately do, I can't predict," Cummings said. "But I think if you are someone looking at it from the point of the view of the ports and the viability of the concession agrement in the Clean Trucks Program, you would be nervous."

Without the concession program, the Clean Trucks Program could lose much of its effectiveness, environmental experts say, as the port would lose an effective way of regulating which trucks can enter and exit. According to port officials, truck emissions rates are roughly 80 percent lower than they were in 2007.

Geraldine Knatz, the port's executive director, said in an interview Friday that the port has only revoked privileges for two or three of more than 900 concession holders since the program began.

"The concession program is very important to the overall success of the Clean Truck Program," Knatz said. "We are going to fight for it."

Sean McNally, a spokesman for the trucking associations, said his group supports many programs that promote more environmentally friendly trucks but objects to policies that allow local and state entities to make regulations regarding the industry. He said industry leaders believe federal law can impose such requirements.

"As our legal department put it, we think it's a chance to makes some good law and really enshrine the ability of the trucking industry to operate without extra burdens imposed on them by states and local entities," McNally said. "We need regulatory uniformity. We need rules at the Port of Los Angeles to be the same as in Long Beach. If every port has its own stickers and placards, that's a problem."

Melissa Lin Perrella, senior attorney with the National Resources Defense Council, which is helping the city of Los Angeles defend the suit, said authorities continue to believe they have the right to invoke some local rules.

"We believe in the Clean Trucks Program, and we believe in its legality," she said. "I think we were all eager to have finality in the case. I would have been quite happy with the case ending with the 9th Circuit's decision. But we'll press on, and we can convince the Supreme Court just like we convinced the 9th Circuit."

Perrella said the case is expected to go to oral arguments in April. And even though recent Supreme Court decisions suggest the justices might side with the trucking industry and rule that federal law supersedes local rules, UCLA's Cummings said it is difficult to predict with certainty which way the court will go.